Provenance of Wild Yeast

[BadRabbit]

I've seen in several books over the last year of baking that the wild yeast in sourdough comes from the actual grain that the flour is made of and does not come from the air in one's kitchen as many believe. The idea of "capturing" wild yeast would therefore be a myth.

If this is true, then is there any real point in making bread this way instead of just buying a known good starter culture? Either way, you are just bringing the wild yeast into your home in a bag as opposed to the romantic notion of capturing a unique blend of wild yeasts native to your home region.

[gfweb]

I've always doubted the yeast in the air theory. Could be true, but given that the technique so often gives good results and airborne yeast would probably vary considerably, I suspect that the yeast comes in with the flour, or the utensils or the hands.

It would be an easy experiment to do. Pasteur did a similar one to disprove the theory of spontaneous generation in the 1800s.

Take two identical bowls of flour and water, leave one open and cover one with foil....wait a few days and look for the bubbling.

Also take some flour and bake it... as well as the bowls and foil to be used for an hour or so at 325 to sterilize it. Mix it with boiled water and a boiled spoon.

If the yeast are airborne both uncovered bowls will begin to ferment. If it comes in with the flour or utensils then only the unsterilized flour bowls will ferment.

[HungryC]

Yeast is definitely in the flour, but it's also in the air (and I sure hope it's not on the utensils or bowl...ick). There's absolutely nothing wrong with a purchased starter, but it will evolve over time to become a local one. IOW, whatever yeasts live/thrive in your area will slowly take over as you add flour & water and air (through the stirring).

[BadRabbit]

Yeast is definitely in the flour, but it's also in the air (and I sure hope it's not on the utensils or bowl...ick). There's absolutely nothing wrong with a purchased starter, but it will evolve over time to become a local one. IOW, whatever yeasts live/thrive in your area will slowly take over as you add flour & water and air (through the stirring).

Why are so many experts claiming that the local yeast theory is incorrect and that ALL the yeast activity comes from the flour?

The changing flavor is easily accounted for by positing that bags of flour (even from the same brand) are likely ground from grains grown in lots of different places. It could be the feeding from different bags of flour over time that causes the change.

Also, I would think that modern air conditioning would eliminate most yeast from the air in a typical kitchen. I use hypoallegenic filters in mine that I would guess removes most larger particles (of which yeast would almost certainly be one).

ETA: I don't think that the presence of yeast in the air is in question. What is unclear is if in the average kitchen there is a strong enough concentration to ever innoculate a starter.

Edited March 22, 2011 by BadRabbit (log)

[BadRabbit]

Take two identical bowls of flour and water, leave one open and cover one with foil....wait a few days and look for the bubbling.

Also take some flour and bake it... as well as the bowls and foil to be used for an hour or so at 325 to sterilize it. Mix it with boiled water and a boiled spoon.

If the yeast are airborne both uncovered bowls will begin to ferment. If it comes in with the flour or utensils then only the unsterilized flour bowls will ferment.

I'm not sure this would necessarily tell you what you want to know. It could be that the baking of the flour would denature the proteins in ways that would make it harder for yeast to break down.

[andiesenji]

This subject has been studied exhaustively by individuals,such as Ed Wood, by Universities, and there have been any number of doctoral theses published with this data, if one cares to look.

And it's not just the wild yeasts but the lactic acid bacteria that ride along with them that produce the flavors.

These studies have been done with sterilized flours - different types to see if different organisms prefer different kinds of grain - and which were the most active, in widely separated areas.

There are starters that prefer multi-milled regular flour, whole wheat and some that are very active with rye and less active with plain wheat so these wild "animals" can be very selective in their tastes. There are some that are highly active with corn and other grains.

Googling "Studies on wild, regional yeasts for sourdough bread" gives 59,400 primary results.

How Stuff Works provides this bit.

I have both ofEd Wood's books and have purchased several of the sourdough starters he offers.

I live in the desert where the concentration of yeasts is somewhat lower and it takes longer to "catch" enough to develop a good culture.

In areas where the humidity is higher (San Francisco and the bay area, for instance) the concentration of the desirable wild yeasts is higher and a culture will develop more rapidly.

If you purchase a sourdough culture from someplace such as South Africa, it will produce a true sourdough for a few months but will eventually be taken over by the "native" yeasts in your area.

I am pretty sure that my sourdough does not develop from the yeasts found in the flour because I routinely "toast" the flour prior to using it in baking because I like the flavor of breads made this way.

Here's another sourdough site.

There are yeasts in flours, however they are not the primary yeasts of the region where the dough is prepared and are rarely strong enough to overcome the native yeasts - that is why purchased cultures revert to the local after some months.

In my opinion, and I am not an expert, some people come up with an idea and run with it without doing any real research and certainly little if any delving into the published data by scientists who actually know what they are doing and keep meticulous records.

Edited March 22, 2011 by andiesenji (log)

[Norm Matthews]

Wild yeast is everywhere. That frosty layer on grape skins is yeast also on some green vegetables and cabbage. Feed those with flour and water and they will develop into usable yeast. Not all is well suited for white bread though. The reason wine first was discovered is because when piled in a barrel, the weight of the upper ones broke the skin on the lower ones allowing the yeast on the surface to come in contact with sugar and liquid inside. Yeast feed on sugar in grape juice and produce carbon dioxide and alcohol. The alcohol is desirable in wine and the carbon dioxide is desirable in making sparkling wine and for rising bread. It does indeed exist everywhere and a yeast grown somewhere else will take on the characteristics of local yeasts eventually

Cultured yeast is delicate and will revert to wild yeast if maintained in a flour and water solution for any length of time.

[HungryC]

Yeast is definitely in the flour, but it's also in the air (and I sure hope it's not on the utensils or bowl...ick). There's absolutely nothing wrong with a purchased starter, but it will evolve over time to become a local one. IOW, whatever yeasts live/thrive in your area will slowly take over as you add flour & water and air (through the stirring).

Why are so many experts claiming that the local yeast theory is incorrect and that ALL the yeast activity comes from the flour?

The changing flavor is easily accounted for by positing that bags of flour (even from the same brand) are likely ground from grains grown in lots of different places. It could be the feeding from different bags of flour over time that causes the change.

Also, I would think that modern air conditioning would eliminate most yeast from the air in a typical kitchen. I use hypoallegenic filters in mine that I would guess removes most larger particles (of which yeast would almost certainly be one).

ETA: I don't think that the presence of yeast in the air is in question. What is unclear is if in the average kitchen there is a strong enough concentration to ever innoculate a starter.

Every time you open a door or window, huge amounts of air enter & exit your house. Even with a HEPA filter on a central AC system, significant amounts of mold, yeast, etc can circulate in the air (as any allergy sufferer can tell you). Your shoes, clothing, AM newspaper, the dog, groceries, the daily mail: any & every object entering your house contains micro-organisms. The bread you bring home from the bakery; the bunch of grapes in the fruit bowl; the potatoes in a basket; the cut flowers in a vase....all are potential sources of "critters" to inoculate a starter culture.

I tried to cultivate a wild-yeast starter multiple times--my earliest failures were due to rampant nasty-bacterial growth...you name the color, and it grew in my starter. Took me a bit of trial & error (and some pineapple juice) to finally tip the balance in favor of yeast. But I live three blocks from the swamp, in an intensely humid atmosphere. Algae, mold, mildew: they're easier to grow than grass around here. I can see how a desert climate might make it significantly harder to cultivate a starter.

[gfweb]

Take two identical bowls of flour and water, leave one open and cover one with foil....wait a few days and look for the bubbling.

Also take some flour and bake it... as well as the bowls and foil to be used for an hour or so at 325 to sterilize it. Mix it with boiled water and a boiled spoon.

If the yeast are airborne both uncovered bowls will begin to ferment. If it comes in with the flour or utensils then only the unsterilized flour bowls will ferment.

I'm not sure this would necessarily tell you what you want to know. It could be that the baking of the flour would denature the proteins in ways that would make it harder for yeast to break down.

It might do that a little, but I'd be surprised if the yeast wouldn't grow in cooked flour to a degree. They are hardy buggers. But if you want to get all rigorous on me , we could just substitute a sterile sugar solution for the flour and see what grows.

[BadRabbit]

Take two identical bowls of flour and water, leave one open and cover one with foil....wait a few days and look for the bubbling.

Also take some flour and bake it... as well as the bowls and foil to be used for an hour or so at 325 to sterilize it. Mix it with boiled water and a boiled spoon.

If the yeast are airborne both uncovered bowls will begin to ferment. If it comes in with the flour or utensils then only the unsterilized flour bowls will ferment.

I'm not sure this would necessarily tell you what you want to know. It could be that the baking of the flour would denature the proteins in ways that would make it harder for yeast to break down.

It might do that a little, but I'd be surprised if the yeast wouldn't grow in cooked flour to a degree. They are hardy buggers. But if you want to get all rigorous on me , we could just substitute a sterile sugar solution for the flour and see what grows.

I had no idea either way. I was just throwing something out there. I am sure that the studies mentioned above controlled for that and andiesenji said she toasts flour ahead of time so it obviously doesn't cause too many issues.

After the response in this thread, I went and looked at a few of the sources. I had thought that I remembered Reinhart being one of them but he says something that seemed to agree with the above hypothesis but after reading it again I don't think he was. He was the most respected of the people I had read that were suggesting it (or I thought were suggesting it in his case).

Hungry C,

Along the same lines as the query about AC, why would a wild yeast be so dominant in a controlled environment like a refrigerator? The inside of my fridge has little in common with my local environment. I can see how a starter kept outside would eventually be taken over by local yeast but I fail to see the advantage my local yeast would have over the wild yeast in the flour when in a fridge.

Also, since my starter in the fridge is mostly covered, it would seem to be exposed much more to the flour used in feeding than any airborne yeast.

Edited March 22, 2011 by BadRabbit (log)

[HungryC]

And the yeast isn't feeding on any proteins, denatured or otherwise, in the flour. Yeast feeds on sugar.

[Big Mike]

I've always had luck making starters by leaving the mixture close to a basket of fruit between feedings. Works every time, I have very active starter in three or four days. I tried earlier this year to make a new one in a different part of my kitchen and didn't get the nearly the same results. There, scientific proof

[PetersCreek]

I watched an interesting episode of Brew Masters (Discovery Channel) a while back in which Dogfish Head brewery was recreating an ancient Egyptian beer called Ta Henket. As I remember it, they went as far as to capture native Egyptian yeasts using petri dishes filled with agar set out in several spots in some village.

[andiesenji]

Wild yeasts can vary widely in activity and not always are "wild" per se.

Until about fifteen years ago, or so, there was a small brewery two miles west of my home and as we have almost constant westerly winds, the movement was from the brewery toward my home and I could often smell it.

My kitchen windows are often open and the screens are certainly not proof against yeasts.

I had been maintaining a particular sourdough culture for a few years with regular feedings and a very dependable behavior.

Sometime during a period of the culture being refreshed and sitting out on the counter under the window, there was apparently an invasion of some yeasts that I suspect originated in the brewery.

The activity increased exponentially. I was away from the kitchen for three hours and when I returned the stuff had filled the 6 quart Cambro container, climbed out and was exploring the counter and down the front of the cabinets. It actually looked like someone had sprayed expanding foam onto the counter.

I had never before had this happen and thought it was a mistake on my part - maybe I had added too much flour or something.

I disposed of all up two cups, added an equal amount of flour and water and put it in the fridge in the cleaned Cambro container.

Even in the fridge it grew to the point that it pushed the lid off the container.

I made bread with it and it was excellent but had an intense beery aroma.

I was able to maintain it for about six months and then it died when I neglected it for too long.

Repeated trials never achieved the same effects, it was a one-off experience.

Then the brewery closed.

[Big Mike]

Too bad about your dead starter, that's what I love about sourdough. I had a starter that I made with organic grapes that tasted awful, it could raise the dead and would triple or quadruple in volume but it was sorta gross.

Have you ever saved starter for long term storage by drying it? I've read you spread it onto parchment paper and leave it in the oven overnight with the light on, then the next day just peel it off and smash it up fine then store in the freezer. I'm bringing one out of cold storage to make some bread this weekend, going to try it to see how it works. It would have saved me from having to start a new one recently when I used all of the starter to make a huge batch of pizza and forgot to leave some start behind

[Norm Matthews]

Yeast does feed on sugar but there are sugars in flour. Sourdough yeast is fed, maintained and kept alive in a batter of flour and water alone. No added sugar.

PS I kept a sourdough starter alive for 15 years.

Edited March 23, 2011 by Norm Matthews (log)

[HungryC]

Hungry C,

Along the same lines as the query about AC, why would a wild yeast be so dominant in a controlled environment like a refrigerator? The inside of my fridge has little in common with my local environment. I can see how a starter kept outside would eventually be taken over by local yeast but I fail to see the advantage my local yeast would have over the wild yeast in the flour when in a fridge.

Also, since my starter in the fridge is mostly covered, it would seem to be exposed much more to the flour used in feeding than any airborne yeast.

Not sure what sort of sourdough-tending regime you follow, but I feed my starter, leave it out at room temp (very loosely covered, generally takes 2-6 hours depending on ambient temp) until it doubles, stir it down, THEN I put it back into the fridge. So it has ample time to absorb anything local floating around.

[BadRabbit]

Hungry C,

Along the same lines as the query about AC, why would a wild yeast be so dominant in a controlled environment like a refrigerator? The inside of my fridge has little in common with my local environment. I can see how a starter kept outside would eventually be taken over by local yeast but I fail to see the advantage my local yeast would have over the wild yeast in the flour when in a fridge.

Also, since my starter in the fridge is mostly covered, it would seem to be exposed much more to the flour used in feeding than any airborne yeast.

Not sure what sort of sourdough-tending regime you follow, but I feed my starter, leave it out at room temp (very loosely covered, generally takes 2-6 hours depending on ambient temp) until it doubles, stir it down, THEN I put it back into the fridge. So it has ample time to absorb anything local floating around.

I do the same but even loosely covered at room temp I would think would keep out most stuff over such a relatively short time (if you were leaving it out for days I could see how the little gaps around the covering would eventually let in enough to make the difference). The only time I could think of that there would be prolonged exposure to air would be in the fridge 2-3 days.

[ScoopKW]

Yeast -- my stock in trade.

"Wild yeast" is often the best stuff in the world -- if you happen to live in Belgium, Bavaria, Marin County, or other areas where the local yeasts do great things -- think Lambic beer, Trappist ale and such.

I remember reading about a couple foreign investors who bought a small brewery in Belgium. The first thing they did was clean all the cobwebs, dust and grime in the brewery. Without the wild yeast, the brewery failed.

Moral, if your local yeast does good things, great! If not, go with a commercial variety and keep it healthy. Yeast needs the proper temperature and just enough sugar and nutrients. Packets of servomyces yeast nutrient will go a LONG way in this regard. Doesn't take much. I use mere grams per 600 gallon batches of beer.

In general, wild yeasts are happier at higher temperatures. You can inhibit their growth by keeping your starter at lower temperatures. Lager beers are the result of colder fermentation. Both yeasts are usually present, but ale yeasts ferment hotter and lagers ferment colder.

Bakers should hit up their local brewpub/microbrewery. Most brewers are HAPPY to pour a pint or two off the bottom of their fermenters. Doesn't cost us a thing, and generates goodwill.